Sealed batteries are roughly classified into cylindrical batteries, prismatic batteries, and pouch batteries according to the shape and the material of housings that contain an electrode body which is a power-generating element. In particular, cylindrical batteries are used in a wide range of applications pertaining to, for example, power tools, electric power-assisted bicycles, and electric vehicles. In these applications, cylindrical batteries are used as assembled batteries in which batteries are connected in series or in parallel.
In the related art, sealing bodies in cylindrical batteries include a mechanism for ensuring safety. For example, Patent Literature 1 discloses a sealing body including a current interrupting mechanism and an explosion-proof valve as illustrated in FIG. 8.
The sealing body 81 illustrated in FIG. 8 is famed by stacking a terminal cap 82, a valve body 83, an insulating member 84, and a metal plate 85 serving as a terminal plate. The valve body 83 has, in its center portion, an annular projection part 83a that projects toward the metal plate 85. The metal plate 85 is connected to the projection part 83a. The insulating member 84 is annularly provided in the vicinity of this connection part so that an outer circumferential portion of the valve body 83 is insulated from an outer circumferential portion of the metal plate 85. Since the valve body 83 receives a battery inner pressure increased by generation of gas inside a battery due to, for example, misuse of the battery, the valve body 83 works so as to pull the connection part in a direction away from the battery. When the battery inner pressure further increases to reach a predetermined value, the connection part fractures to interrupt a current path between the valve body 83 and the metal plate 85. When the battery inner pressure further increases, the valve body 83 fractures so that gas inside the battery is released through a gas port provided in the terminal cap 82.
In the sealing body 81 disclosed in Patent Literature 1, the valve body 83 has a protrusion part 83b that inclines toward the center, and the insulating member 84 has a Z shape in cross section. The insulating member 84 is fitted to the protrusion part 83b, and the metal plate 85 is fitted to the insulating member 84, such that these members are fixed to each other. This structure prevents a fracture of the connection part between the valve body 83 and the metal plate 85 even if the sealing body 81 receives external shock.